Index: Include/object.h
===================================================================
--- Include/object.h	(revision 66078)
+++ Include/object.h	(working copy)
@@ -473,6 +473,7 @@
 PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_SelfIter(PyObject *);
+PyAPI_FUNC(PyObject *) PyObject_NextNotImplemented(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_GenericGetAttr(PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject *,
 					      PyObject *, PyObject *);
Index: Objects/object.c
===================================================================
--- Objects/object.c	(revision 66078)
+++ Objects/object.c	(working copy)
@@ -1286,6 +1286,15 @@
 	return obj;
 }
 
+PyObject *
+PyObject_NextNotImplemented(PyObject *self)
+{
+	PyErr_Format(PyExc_TypeError,
+		     "'%.200s' object is not iterable",
+		     Py_TYPE(self)->tp_name);
+	return NULL;
+}
+
 /* Generic GetAttr functions - put these in your tp_[gs]etattro slot */
 
 PyObject *
Index: Objects/typeobject.c
===================================================================
--- Objects/typeobject.c	(revision 66078)
+++ Objects/typeobject.c	(working copy)
@@ -6057,8 +6057,12 @@
 	}
 	do {
 		descr = _PyType_Lookup(type, p->name_strobj);
-		if (descr == NULL)
+		if (descr == NULL) {
+			if (ptr == (void**)&type->tp_iternext) {
+				specific = PyObject_NextNotImplemented;
+			}
 			continue;
+		}
 		if (Py_TYPE(descr) == &PyWrapperDescr_Type) {
 			void **tptr = resolve_slotdups(type, p->name_strobj);
 			if (tptr == NULL || tptr == ptr)
Index: Objects/abstract.c
===================================================================
--- Objects/abstract.c	(revision 66078)
+++ Objects/abstract.c	(working copy)
@@ -3067,7 +3067,6 @@
 PyIter_Next(PyObject *iter)
 {
 	PyObject *result;
-	assert(PyIter_Check(iter));
 	result = (*iter->ob_type->tp_iternext)(iter);
 	if (result == NULL &&
 	    PyErr_Occurred() &&